InspectAPedia ^®

Here we discuss the advantages and shortcomings of using vacuum cassettes or spore traps to collect mold test samples (or other dust or particle samples) from building wall and ceiling cavities. In this article series discuss the validity of nearly all of the popular mold testing methods currently in use, pointing out the strengths and weakness of each approach to mold sampling in the indoor environment, beginning with air sampling for airborne mold levels indoors. Because mold test validity and mold test accuracy are often confused, readers should also see ACCURACY OF VARIOUS MOLD TEST METHODS. People who need to conduct mold inspection and testing indoors should see MOLD TEST PROCEDURES and TECHNICAL & LAB PROCEDURES.

Our MOLD INFORMATION CENTER includes more broad discussions of the overall approach to building investigation, as do many expert references cited at that web. For a more comprehensive collection information about mold test methods see INDOOR AIR QUALITY METHODS COMPARED. For more on "mold classes" (Cosmetic mold vs. allergenic mold vs. toxic or pathogenic mold) see MOLD CLASSES, HAZARD LEVELS and more references such as a Mold Action Guide are at the end of this document.

© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Validity/Accuracy of Vacuuming Building Cavities for a Hidden Mold Screen

15th Annual North Carolina/South Carolina
Environmental Information Association Technical Conference
Myrtle Beach, SC
Daniel Friedman 23 September 2005, Updated 4/14/2009

Vacuuming building cavities is a popular screening practice to look for mold reservoirs. The investigator is trying to explore wall cavities while doing minimal or no visible damage.

A wall-check™ system has been marketed for this purpose and several manufacturers have coped the basic idea: a receiving Air-o-Cel™ or MCE filter cassette is attached at its inlet side to a tube which is inserted as a probe into a wall cavity, permitting creation of only a small hole. The outlet or pump side of the test device is connected to a pump and operated, typically at 15 lpm. Where we have tested this method we have experimented with both passive collection (what most investigators use) or aggressive collection (banging on the wall/ceiling at various points to attempt to dislodge and stir particles).

Short duration samples, 1-2 minutes using an Air-o-Cell ™ permit a comparatively large number of samples to be collected in a reasonably short interval. Long duration samples, perhaps for up to two hours, are collected using an MCE filter cassette.

Wall Cavity Vacuuming - Found Ineffective

Working with Louis Relle, a Louisiana mold remediation expert on a New Orleans Building which was to be demolished we collected wall-check samples from every suspect Building cavity.

When the building interior surfaces were demolished we then performed a visual inspection and collected bulk surface samples using tape. The wall check samples were completely unable to detect large and significant mold contamination in the cavities of this building.

We postulate that even with mechanical agitation (banging on the wall during wall check sampling) the flow rate of the sampling method does not move enough air to reliably pick up surface contamination unless the mold genera/species happens to be at a particularly high state of active sporulation. The tool remains in the professional's arsenal, to be used with discretion.

Shortcomings of vacuuming building cavities through a tube but our testing strongly suggests that this method is very unreliable for characterizing wall contents. We do not believe that enough air movement is created in the wall cavity (sucking any lpm flow through a small diameter tube) to reliably collect what could be a severe mold reservoir that happens not to be right next to the probe. Further if the cavity is insulated there will be virtually no air or particle movement except from very close to the probe.

What should we make of wall vacuum test results done without other inspection and testing?

Wall cavity vacuum tests, depending on how and when they are performed, can be like searching for a needle in a haystack while looking through a straw: if you find evidence of a problem you're lucky. But if you don't find evidence, when using a very limited-scope method, that doesn't mean that a problem is not there.

Our photo, left, is not showing the wall-check vacuum method that relies on vacuuming into a cassette through a hole in the wall. Instead, here we have pulled loose paneling and have inserted our spore trap cassette into the cavity. This position combined with aggressive sampling by banging on the wall paneling with a flashlight is more likely to collect problem particles if they are present close to the point of vacuum cassette insertion into the wall. But even this approach is not a reliable characterization of mold risk in the building. And it is not looking into the wall cavity itself - rather we are looking at the two surfaces behind the paneling.

Short vacuum pump duration for microscopic examination (to avoid sample overload, e.g. 2-=3 minutes on an Air-O-Cell) does not move enough air to reliably find what may be in the wall cavity. An experiment done with Louis Relle in New Orleans LA demonstrated that wall-vac tests found less than 10% of large problem mold cavities that could be discovered by cutting drywall openings in a building.

Our photo (left) shows a short-duration but larger surface area or wall opening vacuuming system invented and tested by the author - it did not provide useful results.

Longer vacuum pump duration samples for viable sampling (2 hours into an MCE cassette for culturing) still may not move enough air to sample through a cavity, particularly if the cavity is insulated. Further, two-hour samples means that most-likely very few sample points were collected, making the inspection scope extremely limited and thus overall confidence in the accuracy of the picture of the building lower.

Consider that the popularly-marketed version of this wall cavity vacuuming approach to test for hidden mold contamination in buildings relies on culture of the sample. Did you know that only about 10% of molds grow in any culture at all? You're 90% uncertain of the accuracy of the test at the outset. One can't be sure that the mold that grew in the culture represents the dominant problem mold or whether it's just a low-occurrence (in the building) spore that liked the media (in the culture). We like cultures for further genera/species identification of samples but we are nervous about relying on them to tell me if the building has a problem or not.

Share this Article      

...

Technical Reviewers & References

Search InspectAPedia

• Daniel Friedman - principal author/editor of the InspectAPedia^® website
• InspectAPedia Bookstore lists recommended books, organized by topic & available for purchase. Most of our articles also include a list of recommended books for the specific article topic as well as other references, and information sources.
• Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
• Additional technical contributors & reference sources for this article are listed below.

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

MOLD TESTING METHOD VALIDITY
Introduction
  Air samples
    Shortcomings of air sampling
    Mold in Air: Quantitative Analysis
  Tape sampling for mold
    Determination of mold genera
    Determination of mold species
    Shortcomings of tape sampling
  Vacuum samples
    Surface vacuuming
    Shortcomings of surface and carpet vacuuming
    Shortcomings of vacuuming insulation
    Vacuuming building cavities
    Vacuuming exposed insulation
  Cultures to "Test for Mold"
    Shortcomings of culturing
  Swab sampling
  Shortcomings of swab sampling
  PCR methods for Mold Identification
  Mold "Testing" vs. Mold "Problem Identification"
  Are Mold Test Kits Useful?
  Reasons to Test for or Identify Mold
    1. Save Money if it's Just Cosmetic Mold
    2. Mold Related Illness
    3. Mold Cleanup Data baseline

• Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. (727) 595-4211 mark@BestTampaInspector.com

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Books, Complete List of Environmental Inspection, Diagnosis, Cleanup, Air Quality & Design, Inspection, Repair Books at the InspectAPedia Bookstore
• Environmental Health & Investigation Bibliography - our own technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.
• ...

More Information on Building Diagnostic Inspections and Repairs

...

InspectAPedia® Home & Site Map - Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice: In-depth research & advice on diagnosing, testing, correcting, & preventing building defects & indoor environmental hazards. Unbiased information, no conflicts of interest.

The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems

Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to our lab

Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.

Building Inspection, Problem Diagnosis, Forensic Investigation & Testing, Repair Consulting

Contact Daniel Friedman for website content suggestions or for fee-paid consulting